FR2494722A1 - PRECIPITATION-CURABLE ALUMINUM ALLOY ARTICLE AND METHOD OF MANUFACTURE - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS AN ARTICLE IN PRECIPITATION HARDENED ALUMINUM ALLOY AND A MANUFACTURING PROCESS. THE ALLOY CONSISTS OF A SOLID ALUMINUM SOLUTION MATRIX CONTAINING ALFE-BASED CURING PARTICLES, PART OF THE FIRE CONTENT BEING REPLACED BY A REFRACTORY ELEMENT AND THESE PARTICLES HAVE AN AVERAGE SIZE LESS THAN 0.05 MICRON SPREAD EACH OTHER LESS THAN 0.2 MICRON. THE PROCESS CONSISTS OF SOLIDIFYING SUCH ALUMINUM ALLOY WITH A COOLING SPEED EXCEEDING 10CSEC. TO FORM SOLID PARTICLES WHICH BY COMPRESSION ARE TRANSFORMED INTO A UNIT MASS AT A TEMPERATURE LESS THAN 350C. THE INVENTION IS FOR EXAMPLE USEABLE IN APPLICATIONS USING ROTARY MACHINES.

Description

2'494722

  The present invention relates to precipitation hardened aluminum alloy articles and a method of manufacture. More specifically, the invention relates to aluminum alloys treated by the powder metallurgy technique which can be used to form artiles which have usable mechanical properties.

  at high temperatures, at least up to 350 C.

  Attempts have been made in the known art to make improved aluminum alloys by powder metallurgy techniques. These techniques have used increased solidification rates over those generally obtained in conventional molding processes. However, the solidification rates obtained were not large enough to produce metastable phases that can be used in the limited number of alloy systems that have been studied. Articles of the following publications concerning

  the rapid solidification process of aluminum alloys

  : "Exchange of Experience and Information, Structure and Properties of Al-Cr and Al-Fe

  Alloys Prepared by the Atomization Technique ".

  A.A. Bryukhovets, N.N. Barbashin, M.G. Stepanova, and I.N. Fridlyander. Moscow Aviation Technology Institute. Translated by Poroshkovaya Metallurgiya,

  No. 1 (85), pp. 108-111, January 1970.

  "On Aluminum Alloys with Refractory Elements, Ob-

  tained by Granulation "by V.I. Dobatkin and V.I.

  Elagin. Sov. J. NonFerrous Metals / August 1966,

pages 89-93.

  "Fast Freezing by Atomization for Aluminum Alloy Development" by W. Rostoker, R. P. Dudek, C. Freda and R. E. Russell. International Journal

  of Powder Metallurgy. pages 139-148.

  US Patent Nos. 4,002,502, 4,127,426, 4,134,400 and 4,193,822 all relate to aluminum alloys.

  containing iron as the main alloying ingredient.

  In US Pat. No. 4,127,426 there is also described

  rapid solidification of an alloy containing 5% iron.

  It is a principal object of the invention to produce aluminum alloy articles having mechanical properties usable at temperatures

up to at least 3500C.

  It is another object of the invention to describe a class of aluminum alloys which can be processed

  powder metallurgy techniques to obtain

  articles of high resistance.

  Yet another object of the invention is the

  description of the procedures of the metallurgy of powders which

  can be implemented with an aluminum alloy class to obtain articles with properties

  exceptional mechanicals at high temperatures.

  The present invention relates to a new class of aluminum alloy which are cured by a new precipitate. Precipitabon hardened aluminum alloys are known in the art. Such alloys are represented, for example, by alloys based on the copper aluminum system (such as alloy 2024). In such a conventional precipitation precipitation system

  the solubility in the solid state decreases

  health of one element in the other so that a precipitate

  controlled can be reproduced by a heat treatment.

  In the case of the aluminum-copper system the decreasing solid-state solubility of copper and aluminum makes possible the development and control of CuA12 precipitated particles. Since the solubility in the solid state of copper and aluminum increases with temperature, such materials have only limited capabilities to withstand stress at elevated temperatures since the precipitate phase

  tends to dissolve at high temperatures ..

  Another class of alloys that are particle hardened are those alloys known as the SAP type alloy. SAP-type alloy articles are produced by the metallurgical techniques of pudreso the aluminum alloy powder is oxidized

  and then compressed and severely cold-worked.

  - 3 - The result of this treatment is the development of a structure containing discrete fine particles of oxide

  aluminum. Since aluminum oxide is essential

  Tightly insoluble in aluminum, this class of alloy is more stable at high temperatures than alloys.

  precipitation-hardened particles formed by a precipitation phenomenon

  The present invention relates to an alloy class which from certain points of view combines the advantages of the two types of materials previously described.

  of the present invention are cured by a precursor of

  iron-based cipitate and one or more refractory elements

  res. Both iron and refractory elements have an extremely low solubility in the solid state in aluminum

  and for most practical purposes may be considered

  as insoluble in aluminum. As a result, iron-based precipitate particles and refractory elements are quite stable in aluminum even at elevated temperatures. The alloys are prepared by a process that involves rapid solidification from a melt at rates that preferably exceed oC per second. This rapid solidification rate ensures that the precipitate particles, which form upon solidification of the melt, are fine and evenly dispersed. The short period of time involved in the solidification does not allow a significant growth of the particles. If the rate of solidification is sufficiently high, the result will be formation of non-crystalline amine regions and iron and refractory elements. This is a preferred result since

  these amorphous regions can be decomposed in a controlled way.

  by heat treatment to obtain a dispersion

  exceptionally fine precipitate particles.

  Any cooling rate that exceeds 105oC per second will create iron-metal compounds

  refractory which have a metastable structure not in equilibrium.

  In the extreme case, the structure will be amorphous whereas in

  lower cooling speeds a series of different

  non-equilibrium crystalline precipitate structures will occur. It is recognized that precipitates are transformed through these different structures into a balanced structure during exposure to elevated temperatures. The aluminum alloy powder thus produced is compressed to form an article. Various compression techniques may be used provided that the temperature of the alloy does not increase significantly.

  above 3500C during any significant period of time

  catize. In order that the invention can be better understood, reference is made to the following figures: FIG. 1 represents a graph of the limit of breaking strength as a function of the temperature of several usual aluminum and titanium alloys

and an alloy according to the invention.

  Figure 2 shows resistance to elongation

  depending on the temperature of several aluminum alloys

  and titanium and an alloy according to the present invention.

  tion. Figure 3 gives the resistance properties

  at break for a finite duration depending on the temperature

  different aluminum and titanium alloys

  and an alloy of the present invention.

  FIG. 4 shows a photomicrograph of an alloy of the present invention after exposure to a

high temperature.

  Preferred embodiment of the invention

  The alloys according to the invention are based on aluminum

  and contain from 5 to 15% by weight iron and from 1 to% by weight of at least one refractory metal selected from the group consisting of niobium, zirconium, hafnium, titanium, molybdenum, chromium, tungsten and vanadium and mixtures thereof. Preferably the refractory metal is present in an amount of 15 to 35% of the iron content. These refractory elements combine with iron to form a hardening precipitate phase based on A13Fe, the refractory metal partially replacing

some of the iron.

  -5- It is accepted that the invention is in a wide

  measure a discovery of this new phase of hardening

  and many other elements can be added to this alloy for a variety of purposes.

  improved solid solution hardening and resistance

  this to improved corrosion without materially damaging

  the hardening effect that is achieved by means of this new

  veal precipitated according to the invention. The invention is in

  are roughly described as a solid aluminum solution matrix which can contain up to 5% by weight of a solid solution curing element which also contains from 5 to 30% by volume of a hardening precipitate. iron base and at least one of the refractory metals mentioned above. These curing particles have an average diameter of less than 0.05 microns and preferably less than 0.03 microns and are typically spaced from each other by less than 0.2 microns. To our knowledge, such a structure can only be obtained by means of high solidification speeds. To obtain such a structure it is necessary to put the alloys in a molten form with a significant amount of superheating and to solidify this alloy in the form of particles in accordance with a speed exceeding 1050C per second. If we increase the contents

  made of iron and refractory metal, a cooling speed

  Higher cost will be required to achieve the same non-equilibrium structure. Although there are several known techniques that can produce such speeds

  rapid solidification, these techniques are primarily

  mainly for laboratory manufacturing of small quantities of material. The technique which is preferably used to produce commercial quantities of this material is known as the RSR technique. According to this technique a disc disposed is used

  horizontally that is rotated at a speed of about

  20 000-30000 rpm while the material to be atomized is poured on the disc. The rotating disc rejects the material and is then cooled by helium gas jets. The process is described in US Patent No. 4,025,249, 4,053,264 and 4,078,873. Although this is the preferred method, what matters is the cooling rate rather than the characteristics of the process used to obtain the speed of the process. cooling. Another advantage of the preferred process is the cleanliness of the powder that is obtained. Aluminum is a reaction element and it is desirable that the oxidation of the powder is minimized or avoided. This requires a clean process apparatus and the method described above satisfies these requirements. Having produced the material in granular form, this material is then compressed to form an article of usable size. Such compression may be practiced using various methods known to those skilled in the field of metallurgy. A necessary condition

  However, the material is exposed to temperatures

  in excess of 3500C during any significant period of time. Exposures at temperatures above 350 C will result in unwanted magnification

  hardening precipitates and a decrease in

  mechanical tees. Compression techniques that have been successfully implemented include extrusion into

  temperatures around 300OC. Another technique of compression

  What seems practical is the dynamic compression using a shock wave to bind the powder particles together without inducing a significant rise in temperature. As previously indicated, this class of alloy may have a precipitate structure domain

  varying from an amorphous structure to a crystal structure

  line in balance. If solidification rates have been used

  extremely high level so that a substantial amount of

  If the amorphous phase is present, it may be desirable to convert this phase into a more stable crystalline phase in a controlled manner before placing the article in

  service. This can be easily obtained by

  temperature of the compressed article at a temperature between 50 and 300 OC for a sufficient period of time - 7-

  to cause a desired transformation.

  The features of the invention described above can be better understood with reference to the figures. Figures 1, 2 and 3 show the mechanical properties of a specific composition treated according to the present invention in comparison with various existing high strength aluminum alloys and two usual titanium alloys. The compositions of the aluminum alloys are shown in Table I below.

TABLE I

  2014 4.4% Cu, 0.8% Si, 0.8% Mn, 0.4% Mg 2219 6.3% Cu, 0.3% Mn, 0.1% V, 0, 15% Zr 2618 2.3 % Cu, 1.6% Mg, 1.0% Ni, 1.1% Fe 7075 5.6% Zn, 1.6% Cu, 2.5% Mg, 0.3% Cr Such titanium alloys and Aluminum is usually used in applications where high mechanical strength and low density are required. Titanium alloys are generally harder and maintain their strength at higher temperatures than aluminum alloys. However, titanium is much more expensive than aluminum and therefore there is a great deal for higher strength aluminum alloys, especially those that can maintain their resistance to high temperatures. The alloys according to the present invention provide a bridge between

  the gap between the properties of aluminum alloys

  nium and the usual titanium alloys.

  For an application in a rotating machine where the voltages imposed on a component are largely

  the result of the centrifugal force acting on the

  However, it is not so much the absolute mechanical strength that is important but rather the resistance-to-density ratio. It is obvious that a high density article will create greater internal tensions than an identical item of lower density. Titanium alloys are somewhat denser than aluminum alloys. FIGS. 1, 2 and 3 each comprise a dashed line representing a theoretical 8-alloy having the resistance / density ratio of a usual titanium alloy (Ti-6Al-4V) combined with the density of an alloy of typical aluminum. If an aluminum alloy could be developed that could equal or exceed the properties designated by the broken line, such an alloy would be the equivalent of titanium from many points of view for high performance applications, particularly in a machine.

press.

  An alloy composition according to the invention has been prepared from this specific alloy.

  certain mechanical properties have been determined.

  The alloy was a simple alloy containing 8% by weight iron, 2% molybdenum poicide, the balance being aluminum and was prepared using the fast solidification process described above with a cooling rate exceeding 1060C. per second. The result of this cooling process was a powder material which was pressed and heat extruded to produce a material from which test samples were machined. Referring now to FIG. 1, there is shown the breaking strength versus temperature limit for a number of conventional aluminum and titanium alloys. Also shown is a curve illustrating the properties of the A1-8% Fe-2% alloy, Mo previously described as well as the line

  in dashed lines representing the limit of resistance

  this at break of a theoretical alloy having the same strength / density ratio as Ti-6% Al-4% V and the density of aluminum. An aluminum alloy with this

  combination of strength and density could directly

  replace the Ti-6Al-4V alloy in rotary machine applications. It can be seen that in terms of breaking strength at high temperatures the alloy according to the invention is substantially superior to high strength aluminum alloys.

  usual. From temperatures of 100OC and in

_ 9-

  both in the temperature scale, the alloy according to the in-

  vention is more resistant than known aluminum alloys. At elevated temperatures such as 2900C, the superiority of the alloy according to the invention is remarkable, since at 2900C the most resistant known aluminum alloy had a breaking strength limit of about 137.9. MPa whereas the alloy according to the invention has twice this limit of resistance, 275.8 MPa. For purposes of comparison, the theoretical aluminum alloy with the titanium density-to-density ratio would have a breaking strength limit of 413.7 MPa. Therefore, in terms of the breaking strength limit as a function of temperature, the alloy according to the invention makes a bridge between the gap separating the usual alloys.

of aluminum and titanium.

  Figure 2 shows a similar comparison of resistance versus temperature except that the resistance parameter shown is elongation resistance (measured at 0.2%). Again curves are shown for aluminum and titanium alloys

  habit of high resistance and a line in phantom

  broken between the elongation resistance of an alloy having the Ti-6Al-4V density elongation resistance ratio. In terms of elongation resistance the alloy according to the invention (Al-8Fe-2Mo) is very close to the theoretical alloy and is remarkably superior to the usual high strength aluminum alloys. A significant characteristic that is evident in Figure 2 is that the usual high strength aluminum alloys all have a resistance drop in elongation in the temperature range of about 1250C and about 2500C. The alloy according to the invention

  does not show a net decrease in resistance to

  up to a temperature approaching 350 ° C. This is an increase of about 100 ° C in operating temperatures and this is a

  significant advantage of the material according to the invention.

  The increased softening temperature of the alloy according to the invention is an indication of the greater stability

- 10 -

of the alloy.

  Figure 3 shows the resistance properties

  at break for a finite period of various aluminum alloys

  titanium and high strength as a function of temperature. Again, the properties of a theoretical aluminum alloy having the resistance ratio to

  density of Ti-6% Al alloy, 4% V are also shown.

  The curves shown indicate the voltage required at a given temperature to produce a break in a sample after 1000 hours of exposure. Again it can be seen that the alloy according to the invention is superior,

  to the usual high strength aluminum alloys.

  Figure 4 is an electron-transmitting micrograph of the 8Fe-2Mo aluminum material described above after exposure to 290 C for 4 hours. The significant characteristic that we can see in the

  microphotography is that the precipitate phase is extremely

  even after exposure to temperatures and

  which would produce substantial softening in all usual alumium alloys. It can be generally seen that the structure of the precipitate is of the order

  of 0.01 micron in size after this treatment.

  The alloys according to the invention also

  higher elasticity moduli than aluminum alloys

  usual minium. The modulus of elasticity is related to the stiffness of the alloy and the high values of the

  Modules are desired for structural applications.

  The usual alumi- nium alloys have modulus values of about 68950 MPa and the usual titanium alloys have moduli between 96530 and 110320 MPa. The value measured for the modulus of the previously described alloy A1-8% Fe-2%

  Mo es; t85498 MPa. The valeum domain of elastic moduli

  for the alloys according to the invention will be 82740 -

110320 MPa.

  Of course various modifications can be

  made by those skilled in the art to aluminum alloy articles -

  and manufacturing processes which have just been dispensed as a non-limitative example

of the scope of the invention.

- he -

Claims (7)

claims:   1. High strength alumirdam alloy article consisting essentially of an aluminum solid solution matrix containing a dispersion of hardening particles characterized in that said particles are based on a   composed of Al3Fe, part of the Fe content being replaced by   by a refractory element selected from the group consisting of   titanium, zirconium, hafnium, niobium, molybdenum, tungsten, chromium and vanadium and their   mixtures, these particles having an average size inferior   re at 0.05 microns and a mean spacing between particles less than 0.2 microns.   2. Aluminilm alloy article according to the   cation 1, characterized in that the average dimension of   particles is less than 0.03 microns.   3. Aluminum alloy according to claim 1 characterized in that the curing phase is present   in an amount of 5 to 30 percent by volume.   4. Aluminum alloy according to claim 1,   characterized in that the refractory element is molybdenum.   5. A method of manufacturing a high strength aluminum alloy article characterized in that it comprises the steps of a. solidifying an aluminum alloy containing 5 to 5 percent by weight of iron and 1 to 5 percent of a refractory element selected from the group consisting of titanium, zirconium, hafnium, niobium, molybdenum, tungsten, chromium, vanadium and their mixtures to a   speed exceeding 105oC / sec to form solid particles.   b. consolidate solid particles into a mass   unit at a temperature below 3500C.   6. Method according to claim 5, characterized in that the refractory element is present in a quantity from 15 to 35% of the iron content.   7. Method according to claim 5, characterized   in that the refractory element is molybdenum. 407 E - T 'L' 4 0